青藏高原矮嵩草草甸和金露梅灌丛草甸CO2通量变化与环境因子的关系

利用涡度相关技术观测了青藏高原两个典型的生态系统即矮嵩草(K obresia hum ilis)草甸和金露梅(P oten-tilla f ruticosa)灌丛草甸的CO2通量,并就2003年8月份的数据,分析了生态系统通量变化与环境因子的关系.8月份是这两个生态系统的叶面积指数达到最高也是相对稳定的时期,在此期间矮嵩草草甸和金露梅灌丛草甸净碳吸收量分别达56.2和32.6 g C.m-2,日CO2吸收量最大值分别为12.7μm o l.m-2.-s 1和9.3μm o l.m-2.-s 1,排放量最大值分别为5.1μm o l.m-2.-s 1和5.7μm o l.m-2.-s 1.在相同光合有效光量子通量密度(PPFD)条件下,矮嵩草草甸CO2吸收速度大于金露梅灌丛草甸;在PPFD高于1 200μm o l.m-2.s-1的条件下,随气温增加,两生态系统的CO2吸收速度都下降,但矮嵩草草甸的下降速度(-0.086)比金露梅灌丛草甸(-0.016)快.土壤水分影响土壤呼吸,并且影响差异因植被类型不同而不同.生态系统日CO2吸收量随昼夜温差增加而增大;较大的昼夜温差导致较高的净CO2交换量;植物反射率与CO2通量之间存在负相关关系.     

增温对青藏高原高寒草甸生态系统固碳通量影响的模拟研究

低温被广泛认为是高寒草甸生态系统首要限制性因子,因此增温可能会在某种程度上促进初级生产力,但是也可能由于土壤水分、N素营养状况的改变形成新胁迫而抑制生产力提高。此外,生态系统呼吸由于增温而提高的幅度也可能高于初级生产力提高的幅度,造成总碳库平衡的改变。利用青藏高原海北高寒草甸实测数据对生态系统过程模型Biome-BGC(V.4.2)进行了参数化,并利用研究区实测土壤水分(0-40 cm)和其它观测数据对模型进行了检验,证明模型模拟结果较为可靠。模型使用2005-2008年的海北气象站实测气象数据包括气温、降水等作为驱动数据,模拟了增温1.2-1.7℃下青藏高原海北定位站高寒草甸生态系统碳通量的变化,并整合分析增温试验平台上已发表的试验,与模拟结果进行对比,探讨增温对海北高寒草甸生态系统碳收支的可能影响。结果表明:2005-2008年青藏高原高寒草甸生态系统为弱的碳汇,短期增温导致系统净碳固定增加。增温直接影响系统碳通量,也通过土壤水分和土壤矿化氮变化间接影响碳通量,相比土壤水分和氮素,增温对影响碳通量变化过程中的效应更大;研究也揭示,在增温条件下,植物对土壤矿化氮的吸收量小于有机质分解产生的土壤矿化氮量,土壤矿化氮含量增加。     

氮素添加对内蒙古草甸草原生态系统CO2交换的影响

氮沉降增加将影响草原生态系统固碳, 但如何影响草原生态系统CO₂交换目前为止还没有定论。同时, 不同类型和剂量氮素对生态系统CO₂交换影响的差异也不明确。选取内蒙古额尔古纳草甸草原, 开展了不同类型氮肥和不同剂量氮素添加条件下生态系统CO₂交换的野外测定。实验设置尿素和缓释尿素2种类型氮肥各5个剂量水平(0、5.0、10.0、20.0和50.0 g N·m^-2·a^-1)。结果显示, 生长季初期及中期降雨量低时, 氮素添加抑制生态系统CO₂交换; 而生长季末期降雨量较高时促进生态系统CO₂交换。随着氮素添加水平的提高, NEE和GEP均显著增加, 当氮素添加量达到10 g N·m^-2·a^-1时, NEE和GEP的响应趋于饱和。2种氮肥(尿素和缓释尿素)仅在施氮量为5 g N·m^-2·a^-1时, 缓释尿素对生态系统CO₂交换的促进作用显著大于尿素, 在其它添加剂量时差异不显著。研究结果表明: 氮素是该草甸草原生态系统的重要限制因子, 但氮沉降增加对生态系统CO₂交换的影响强烈地受降雨量与降雨季节分配的限制, 不同氮肥(尿素和缓释尿素)对生态系统CO₂交换作用存在差异。     

不同幅度的实验增温对藏北高寒草甸净生态系统碳交换的影响

全球气候变暖将对陆地生态系统(尤其是高寒草甸生态系统)碳循环产生深远影响。该研究依托中国科学院地理科学与资源研究所藏北高原草地生态系统研究站(那曲站), 设置不同增温幅度实验, 模拟未来2 ℃增温和4 ℃增温的情景, 探究不同增温幅度对青藏高原高寒草甸净生态系统碳交换(NEE)的影响。研究结果显示: 1)在2015年生长季(6-9月), 不增温和2 ℃增温处理下NEE小于0, 总体表现为碳汇, 而4 ℃增温处理下NEE大于0, 总体表现为碳源; 2)在生长季的6月、8月及整个生长季, 与不增温相比, 4 ℃增温处理显著提高了NEE, 而2 ℃增温处理没有显著改变NEE; 7月, 2 ℃和4 ℃增温处理均显著提高了NEE; 3)在半干旱的高寒草甸生态系统, 土壤水分是决定NEE的关键因素, 增温通过降低土壤水分而导致高寒草甸生态系统碳汇能力下降。该研究可为青藏高原高寒草甸生态系统应对未来气候变化提供基础数据和理论依据。     

青藏高原高寒草甸生态系统净二氧化碳交换量特征

高寒草甸是青藏高原广泛分布的植被类型之一,面积约120万km2,地处青藏高原腹地的当雄草原站即位于该类植被的典型分布区。以2003年8~10月中旬在该站用涡度相关法连续观测的CO2通量数据资料为基础,分析了高寒草甸生态系统8~10月份净二氧化碳交换量(NEE)的日变化规律,及其与光合有效辐射、降水、温度等环境因子之间的关系。结果表明,8~10月份的日均NEE有明显的日变化,表现为单峰型,通常在地方时11:00~12:00左右达到碳吸收的最大值,平均为-0.2680mgCO2/(m2·s)(-6.0800μmolCO2/(m2·s))。白天的NEE与光合有效辐射之间符合很好的直角双曲线关系,表观量子产额平均为0.0203μmolCO2/μmolPAR,表观最大光合速率平均为9.7411μmolCO2/(m2·s)。夜晚的NEE与5cm地温有很好的指数函数关系。     

青藏高原高寒灌丛非生长季节CO2通量特征

利用2003年和2004年涡度相关系统通量观测资料,对青藏高原高寒灌丛非生长季节CO2通量特征及其主要影响因子进行了分析。(1)从净生态系统CO2交换(NEE)日变化特征看,除13:00~19:00时有较小的CO2净释放以外,其余时段NEE均很小;(2)高寒灌丛非生长季月份间NEE差异明显,4月和10月是CO2净释放量较大,1月和12月CO2净释放量较小;(3)相对温带草原(高杆草大草原)草地类型,低温抑制下的青藏高原高寒灌丛生态系统非生长季节日平均CO2释放率较低;(4)高寒灌丛非生长季NEE日变化模式与5 cm土壤温度变化呈显著正相关,土壤温度是影响非生长季节青藏高原高寒灌丛NEE变化的主导气候因子,同时NEE变化还受降水的影响。     

长江源区高寒草原和高寒草甸土壤粒径分布特征

为探究长江源区主要下垫面土壤空间异质性与粒径分布(PSD)非均匀性,运用分形理论描述高寒草原和高寒草甸2种下垫面土壤粒径分布特征,分析了 2种下垫面土壤的分形维数特征差异及其与土壤颗粒组成的关系.结果表明:研究区土壤颗粒粒径主要分布于100-800 μm,高寒草原土壤单重分形维数(Dv)为2.429～2.508,高寒草...     

青藏高原高寒草甸初级生产力及其主要影响因素

青藏高原有各类天然草地14×108hm2,其中高寒草甸和高寒灌丛约占青藏高原天然草地面积的50%,占全国草地总面积的16.2%。嵩草草甸是高寒草甸的主体,包括矮嵩草草甸、金露梅灌丛草甸、藏嵩草草甸、小嵩草草甸和高山嵩草草甸等,这5类高寒草甸平均地上生物量分别为354.2、422.4、445.1、227.3和368.5g/m2,地下生物量分别为3389.6、3548.3、11922.7、4439.3、5604.8g/m2,地下与地上生物量的比例分别为10.55、10.15、27.82、14.82和15.21,远大于IPCC(2006)报告中地下/地上生物量比例的默认值(2.8±95%)。地下生物量对气候变化和放牧的反应比地上生物量更敏感,干旱和重度放牧均降低了地下/地上生物量的比例。在极度退化状态下地下/地上生物量的比例2。对于轻度和中度退化的高寒草甸应以围封禁牧为主要恢复措施,但如果结合补播和施肥,则恢复速率会加快;对于重度和极度退化的高寒草甸,由于草地植物群落中优良牧草的比例极低,仅靠自然恢复很难进行恢复或需要的年限很长,所以必须采用人工重建的措施,并结合毒杂草防除和施肥等措施进行恢复,通过建立人工或半人工草地的措施予以重建。     

系统发育多样性对青藏高原高寒草甸的稳定性影响

生物多样性较高的草地生态系统能够充分利用生态环境资源,提升生态系统的多功能性。本文以青藏高原高寒草甸生态系统为研究对象,基于多元线性回归和结构方程模型,阐明系统发育多样性、物种多样性和环境因素对高寒草甸生态系统稳定性的影响。结果表明：高寒草甸系统发育多样性、物种多样性和环境因素与生态系统稳定性之间均存在正相关关系,且具有尺度依赖性。小样方尺度高寒草甸通过物种多样性(丰富度指数)和环境因素对生态系统稳定性产生影响,作用系数分别为0.237和0.221。系统发育多样性主要受到物种多样性影响,作用系数为0.812(P<0.001)。大样方尺度生态系统稳定性主要受到环境因素、物种多样性影响,作用系数分别为0.364和0.246(P<0.05)。随着样方尺度的增大,高寒草甸的系统发育多样性、物种多样性和环境因素对生态系统稳定性的影响逐渐增强,且环境因素的作用效应逐渐占据主要地位。因此,应充分注重系统发育多样性和物种多样性在维持高寒草甸生态系统稳定性的作用。     

一次降水过程对青藏高原高寒草甸CO2通量和热量输送的影响

青藏高原高寒草甸的热量输送和碳收支对气候变化的响应十分敏感,降水过程对其影响较为复杂。利用三维超声风速仪和红外CO2／H2O分析仪,以及常规微气象要素的涡度相关观测系统,分析了2002年8月8—17日的一次降水过程对青藏高原高寒草甸CO2通量和热量输送的影响。结果表明：降水过程使气温、地温和辐射等有所降低,大气湿度和CO2通量有所升高;气温、地温、总辐射、地表反射辐射、光合有效辐射（PAR）、净辐射、土壤热通量、潜热通量和显热通量分别下降了23．3％、23．1％、61．9％、58．9％、61．7％、57．9％、268．3％、61．6％和71．0％,大气湿度和CO2通量分别升高了27．0％和38．6％;降水削弱了PAR对白天净生态系统CO2交换量（NEE）的影响,而增加了地温对夜间呼吸的控制;降水强度对白天NEE几乎没有影响,但能降低夜间呼吸。     

Carbon Dioxide Exchange Between the Atmosphere and an Alpine Shrubland Meadow During the Growing Season on the Qinghai-Tibetan Plateau

Abstract: In the present study, we used the eddy covariance method to measure CO₂ exchange between the atmosphere and an alpine shrubland meadow ecosystem (37°36'N, 101°18'E; 3 250 m a.s.l.) on the Qinghai-Tibetan Plateau, China, during the growing season in 2003, from 20 April to 30 September. This meadow is dominated by formations of Potentilla fruticosa L. The soil is Mol-Cryic Cambisols. During the study period, the meadow was not grazed. The maximum rates of CO₂ uptake and release derived from the diurnal course of CO₂ flux were -9.38 and 5.02 μmol·m^-2·s^-1, respectively. The largest daily CO₂ uptake was 1.7 g C·m^-2·d^-1 on 14 July, which is less than half that of an alpine Kobresia meadow ecosystem at similar latitudes. Daily CO₂ uptake during the measurement period indicated that the alpine shrubland meadow ecosystem may behave as a sink of atmospheric CO₂ during the growing season. The daytime CO₂ uptake was correlated exponentially or linearly with the daily photo synthetic photon flux density each month. The daytime average water use efficiency of the ecosystem was 6.47 mg CO₂/g H₂O. The efficiency of the ecosystem increased with a decrease in vapor pressure deficit.
(Managing editor: Ya-Qin HAN)     

Carbon Dioxide Exchange Between the Atmosphere and an Alpine Shrubland Meadow During the Growing Season on the Qinghai-Tibetan Plateau

In the present study, we used the eddy covariance method to measure CO2 exchange between the atmosphere and an alpine shrubland meadow ecosystem (37°36′ N, 101o18′ E; 3 250 m a.s.l.) on the Qinghai-Tibetan Plateau, China, during the growing season in 2003, from 20 April to 30 September. This meadow is dominated by formations ofPotentillafruticosa L. The soil is Mol-Cryic Cambisols. During the study period, the meadow was not grazed. The maximum rates of CO2 uptake and release derived from the latitudes. Daily CO2 uptake during the measurement period indicated that the alpine shrubland meadow ecosystem may behave as a sink of atmospheric CO2 during the growing season. The daytime CO2 uptake was correlated exponentially or linearly with the daily photosynthetic photon flux density each month. The daytime average water use efficiency of the ecosystem was 6.47 mg CO2/g H2O. The efficiency of the ecosystem increased with a decrease in vapor pressure deficit.     

三江源地区人工草地的生态系统CO2净交换、总初级生产力及其影响因子

为了揭示三江源区垂穗披碱草(Elymus nutans)人工草地生态系统(100°26′-100°41′ E, 34°17′-34°25′ N, 海拔3 980 m)的净生态系统CO₂交换(NEE), 该研究利用2006年涡度相关系统观测的数据分析了该人工草地的NEE, 总初级生产力(GPP)、生态系统呼吸(R_eco)以及R_eco/GPP的变化特征及其影响因子。CO₂日最大吸收值为6.56 g CO₂·m^-2·d^-1, 最大排放值为4.87 g CO₂·m^-2·d^-1。GPP年总量为1 761 g CO₂·m^-2, 其中约90%以上被生态系统呼吸所消耗, CO₂的年吸收量为111 g CO₂·m^-2。5月的R_eco/GPP略高于生长季的其他月份, 为90%; 6月R_eco/GPP比值最低, 为79%。生态系统的呼吸商(Q₁₀)为4.81, 显著高于其他生态系统。该研究表明: 生长季的NEE主要受光量子通量密度(PPFD)、温度和饱和水汽压差(VPD)的影响, 生态系统呼吸则主要受土壤温度的控制。     

青藏高原两种高寒草地植被变化及其水温驱动因素分析

高寒草甸和高寒草原作为青藏高原两种重要植被类型,研究其植被变化与气候变化相关性,有助于为青藏高原两种高寒草地生态系统应对全球气候变化管理提供参考。以位于同纬度的三江源高寒草甸和阿里高寒草原为研究对象,基于植被净初级生产力(Net Primary Productivity, NPP)变化表征植被变化,利用NPP数据和气象数据,分别分析两地2000—2017年植被NPP、降水和气温时空变化差异;利用Sen+Mann-Kendall趋势检验,研究两种高寒草地气候与植被净初级生产力变化趋势;以县域统计年鉴牛羊肉产量表征放牧强度,研究放牧活动对高寒草地植被变化的影响;通过Pearson相关和偏相关分析方法,分别研究降水和气温对两种高寒草地植被NPP变化影响差异。研究结果表明:(1)2000—2017年三江源高寒草甸和阿里高寒草原区年平均气温以0.085℃/a和0.084℃/a的趋势上升,降水以平均每年3.87 mm和2.23 mm的趋势增加,高寒草甸区变暖变湿速率较高寒草原区快。(2)三江源高寒草甸和阿里高寒草原植被NPP均呈现由东南向西北逐渐降低空间格局;2000—2017年高寒草甸区57.7...     

Paired comparisons of carbon exchange between undisturbed and regenerating stands in four managed forests in Europe

The effects of harvest on European forest net ecosystem exchange (NEE) of carbon and its photosynthetic and respiratory components (GPP (gross primary production) and TER (total ecosystem respiration)) were examined by comparing four pairs of mature/harvested sites in Europe via a combination of eddy covariance measurements and empirical modeling. Three of the comparisons represented high coniferous forestry (spruce in Britain, and pines in Finland and France), while a coppice‐with‐standard oak plantation was examined in Italy. While every comparison revealed that harvesting converted a mature forest carbon sink into a carbon source of similar magnitude, the mechanisms by which this occurred were very different according to species or management practice. In Britain, Finland, and France the annual sink (source) strength for mature (clear‐cut) stands was estimated at 496 (112), 138 (239), and 222 (225) g C m^?2, respectively, with 381 (427) g C m^?2 for the mature (coppiced) stand in Italy. In all three cases of high forestry in Britain, Finland, and France, clear‐cutting crippled the photosynthetic capacity of the ecosystem – with mature (clear‐cut) GPP of 1970 (988), 1010 (363), and 1600 (602) g C m^?2– and also reduced ecosystem respiration to a lesser degree – TER of 1385 (1100), 839 (603), and 1415 (878) g C m^?2, respectively. By contrast, harvesting of the coppice oak system provoked a burst in respiration – with mature (clear‐cut) TER estimated at 1160 (2220) gC m^?2– which endured for the 3 years sampled postharvest. The harvest disturbance also reduced GPP in the coppice system – with mature (clear‐cut) GPP of 1600 (1420) g C m^?2– but to a lesser extent than in the coniferous forests, and with near‐complete recovery within a few years. Understanding the effects of harvest on the carbon balance of European forest systems is a necessary step towards characterizing carbon exchange for timberlands on large scales.     

Carbon Balance in an Alpine Steppe in the Qinghai-Tibet Plateau

Carbon fluxes were measured using a static chamber technique in an alpine steppe in the Qinghai-Tibet Plateau from July 2000 to July 2001. It was shown that carbon emissions decreased in autumn and increased in spring of the next year, with higher values in growth seasons than in winters. An exponential correlation （Ecarbon = 0.22（exp（0.09T） ＋ In（0.31P ＋ 1））, R^2 = 0.77, P 〈 0.001） was shown between carbon emissions and environmental factors such as temperature （T） and precipitation （P）. Using the daily temperature （T） and total precipitation （R）, annual carbon emission from soil to the atmosphere was estimated to be 79.6 g C/m^2, 46% of which was emitted by microbial respiration. Considering an average net primary production of 92.5 g C/m^2 per year within the 2 year experiment, alpine steppes can take up 55.9 g CO2-C/m^2 per year. This indicates that alpine steppes are a distinct carbon sink, although this carbon reservoir was quite small.     

Carbon Balance in an Alpine Steppe in the Qinghai-Tibet Plateau

Carbon fluxes were measured using a static chamber technique in an alpine steppe in the Qinghai-Tibet Plateau from July 2000 to July 200t. It was shown that carbon emissions decreased in autumn and increased in spring of the next year, with higher values in growth seasons than in winters. An exponential correlation (Ecarbon = 0.22(exp(0.09T) + In(0.31P + 1)), R2 = 0.77, P < 0.001) was shown between carbon emissions and environmental factors such as temperature (T) and precipitation (P). Using the daily temperature (T) and total precipitation (R), annual carbon emission from soil to the atmosphere was estimated to be 79.6 g C/m2, 46% of which was emitted by microbial respiration. Considering an average net primary production of 92.5 g C/m2 per year within the 2 year experiment, alpine steppes can take up 55.9 g CO2-C/m2 per year. This indicates that alpine steppes are a distinct carbon sink, although this carbon reservoir was quite small.     

Radon fluxes in tropical forest ecosystems of Brazilian Amazonia: night-time CO2 net ecosystem exchange derived from radon and eddy covariance methods

Radon‐222 (Rn‐222) is used as a transport tracer of forest canopy–atmosphere CO₂ exchange in an old‐growth, tropical rain forest site near km 67 of the Tapajós National Forest, Pará, Brazil. Initial results, from month‐long periods at the end of the wet season (June–July) and the end of the dry season (November–December) in 2001, demonstrate the potential of new Rn measurement instruments and methods to quantify mass transport processes between forest canopies and the atmosphere. Gas exchange rates yield mean canopy air residence times ranging from minutes during turbulent daytime hours to greater than 12 h during calm nights. Rn is an effective tracer for net ecosystem exchange of CO₂ (CO₂ NEE) during calm, night‐time hours when eddy covariance‐based NEE measurements are less certain because of low atmospheric turbulence. Rn‐derived night‐time CO₂ NEE (9.00±0.99 μmol m^?2 s^?1 in the wet season, 6.39±0.59 in the dry season) was significantly higher than raw uncorrected, eddy covariance‐derived CO₂ NEE (5.96±0.51 wet season, 5.57±0.53 dry season), but agrees with corrected eddy covariance results (8.65±1.07 wet season, 6.56±0.73 dry season) derived by filtering out lower NEE values obtained during calm periods using independent meteorological criteria. The Rn CO₂ results suggest that uncorrected eddy covariance values underestimate night‐time CO₂ loss at this site. If generalizable to other sites, these observations indicate that previous reports of strong net CO₂ uptake in Amazonian terra firme forest may be overestimated.